Electron discharge tube circuit arrangement



Nov. 13, 1951 E. GREEN ELECTRON DISCHARGE TUBE CIRCUIT ARRANGEMENT Filed Oct. 18, 1947 2 SHEETS'-SHEET l v Snventor Zrneswen Q M (Ittomeg I Nov. 13, 1951 E. GREEN. 7

ELECTRON DISCHARGE TUBE CIRCUIT ARRANGEMENT 2 SHEETSSHEET 2 Filed Oct. 18, 194'? IVE TWO/PK Znventor Ernest Green attorney Patented Nov. 13, 1951 ELECTRON DISCHARGE TUBE CIRCUIT ARRANGEMENT Ernest Green, Chelmsford, England, assignor to Radio Corporation of America, a corporation of Delaware Application October 18, 1947, Serial No. 780,735 In Great Britain October 18, 1946 2 Claims. 1

This invention relates to electron discharge tube circuit arrangements and more specifically to such arrangements employing stages of the so-called grounded grid type.

Triodes are coming into increasingly-common use as grounded grid amplifiers, more particularly for high frequency work, mainly because of the relatively great circuit simplicity of the grounded grid type of connection. Known arrangements have the defect, however, that the effective output impedance of the grounded grid stage is often not what is required, for. in the usual case in which the driving source for thestage is of very small or negligible impedance, the

output impedance approximates the plate resistance of the tube.

The present invention seeks to overcome this defect and to provide improved grounded grid amplifier Or the like arrangements wherein a desired effective output impedance can be obtained and, in particular, wherein an effective output impedance which is large relative to the load impedance can be obtained.

According to this invention a grounded grid amplifier or other circuit arrangement comprises a grounded grid stage which is drivenby a source whose impedance is of predetermined value chosen in dependence upon the effective output impedance required. Where a variable output impedance is required the driving source may be arranged to be of variable. impedance.

The driving source may take any of a variety of forms, e. g. it may be a screen grid tube, pentode, or similar tube or tubes; or it may be constiv tuted by the combination of a low impedance stage with an impedance inverting network which couples said stage to the driven grid stage so as to present a high source impedance to said stage; or it may be constituted by another grounded grid stage with a high input impedance or by a cascaded series of such stages.

The invention is illustrated in and further explained in connection with the accompanying drawings in which Fig. 1 is an explanatory diagrammatic figure which will be referred to in the mathematical exposition which follows and the remaining figures are diagrams showing embodiments of the invention. Where possible like references are used for like parts throughout the figures.

Referring to Fig. 1, it will first be shown that the effective output impedance of a'grounded grid stage (comprising triode VI in Fig. 1) depends on the impedance of the source driving a 2 that stage on the input side and therefore, by making the source impedance high the stageoutput impedance may be made high. Let: I1=fundamental component of current, common both to the input circuit and the load. ZL=load impedance. Ez=output volts from the stage across the tuned circuit L2, C2 and the load Zn. E1=input volts to the stage across the tuned circuit Ll, C l. a Es=internal E. M. F. of the driving source. Zs=eifective impedance of the driving source. Z1=effective impedance of the input to the stage. Zz=e1fective impedance of'the output of the stage. R =plate resistance of the tube in the stage, and u=amplificati0n factor of the tube.

Then, for the grounded grid arrangement (,u|1)E1=(R -|ZL) I1 (1) so that E1 RI +ZL I Z and for the input side Er (Z.+ .)I. (z.+ M1 )1. (l"+ -1 pi s(I- l+ 1 This is the equation of a generator withinternal E. M. F. of Es and internal impedance (R +Zs( .+1)) operating into a load Zr... Thus the effective output impedance Z2 is given by:

If, therefore Z5 is negligible or very small (the common case) but by making ZS large Z2 can be made large. For example, by taking a value of 5000 ohms for Zs for a tube with a value of 50 it is possible to add over 250,000 ohms to the effective output impedance.

Referring to Fig. 2 which shows one embodiment of the invention suitable for use on low frequency, a grounded grid triode'Vl has its cathode connected to earth through a resistanceRl across which input is applied and its grid earthed through a suitable condenser (30 and biased from a suitable source (not shown) connected at (33-. Anode potential is applied in any convenient way, e. g. through a choke CH2 and the anode is'connected to one end ofthe load represented by the rectangle Zx. which is earthed at the other end.

In accordance with this invention the driving source of the triode is constituted by a screen grid tube V2 whose anode is condenser coupled by condenser CC to the cathode of the triode VI and whose cathode is earthed through a resistance R3. ilheainputwave tc.be,,amplified-.is applied atiIN: acrossaeresistance 1R2.-(or TQtheI-impedance in the control grid circuit of the screen grid tube) whose electrodes receive operating D. C. poentials in any convenient well known way, for example as conventionally shown.

Fig. 3 shows a modification suitable -=for-'use on high frequencies. Here paralleL-tunedzcircuits Ll, Cl and L2, C2 are connectedrespectively-hetween the cathode of the grounded grid triode VI and earth and the anode .of. said triode .and earth, the latter connection including,.;of course, a blocking condenser BC in the case'illustrat'ed in which anode potential is applied toLthe tniode through the coil in the anode tuned circuit. The

;-..catho de ,tuned; circuit L1 replaces the, cathode legresistanceiR I. oi Eig 2. Thesetwotunedcircuits serve to tune out, respectively, the output c irc uit andr input circuitcapacities. .TIhe-cathode of; the triodeVI;.igcapacity. coupledby. condenser CC to a point on the. anode tuned circuit ;of; ascreen.;g1;id.tube--V2. whichsreceives. the input wave on its;control grid across the-usual .egrid -.tunedcircuit,GLC.

As already stated, the driving source ,for the grounded; grid stage; may: be constituted .by a cathode followencoupled to said sta e-through -,-,an::impedance inverting. network, e. g.- arrealor ex-artificial linea quarter "or an odd multiple. of .qa quarterwvave lengthlong.

In the embodimentaof-Eig-d thegrounded grid or driven-stageconsists:of two triodes VI, .VI' in balanced arrangement with a tuned circuit Ll,

' Cl between theirqcathodes and another tuned circuit L2, C2 in parallel with the load ZLlbetween their anodes. The input or driving source con- ;sists of two triodes 'V2,1 V2.' arranged in a balanced cathode follower circuit coupled to the grounded grid triode stage:.through.-;a load-inverting network which includes the tuned circuit LI Cl and a tuned circuit DLC between the cathodes of the driving stage V2, V2.

In a .further' type :of embodiment a plurality of generallyosimilar groundedgrid tubes incascade is.employedgthejcathodeof each tube. (except the 'ifirst) .being. capacity coupled to a suitable point ,oni the tuned anode circuit of the ..preceding ,and

" the first tube having a'high input impedanceconstituted, for example, by a resistance connected tc the input cathodezzlZn-Fig. '5, which illustrates an .embodiment, oLthis type, thegrounded grid stage VI having the tuned 'circuit Ll,. Cl. in its cathode leg is capacity coupled by condenser CC to a tap on the coil of the anode tuned circuit PAL-C1011; a; preceding-grounded grid stage, includ- -.--ing triode- .V2. ,having a .tunedcircuit-LT, C24, in

its. .cathodeleg, and. a .high resistance -;HR .con-

.-. nected to thesinputcathode.

Although, in the foregoing description;.ampli- .::fi.ers operating. as so-called ,,c1ass A: amplifiers ..wi.thout, grid. current. have. .-.been;v assumed ..(the

. preceding. mathematical .theory fits this case) the invention is. also .applicableto other; cases, .i.v e.. to

...tuhes operating in .classB or class Cwith or withoutzgridcurrent- The main efiectoi gridcurrent is .somewhat to reduce. ,thelefiective ,source, im-

pedance.

An important a lication of thisinvention is to provide. astage. havin a..high. efie'ctive output impedance in. arrangement. wherein. such. a

4 stage is employed in combination with a load inverting network, e. g. a quarter wave line (that is to say a line one quarter, or an odd multiple of one quarter, of a wave length long electrically), 5 to act as a low impedance source feeding into a varyingload. ,A partioulanexampleof this is in .connectiongwith a television transmitter using grounded grid amplifiers, with a grid modulation .;applied to one of the stages. In such a case the load on the stage preceding the modulated stage --varies-from-a-lieavy load at full output to zero atzero output. Fig. 6 illustrates one embodiment ..i --which...the ,present invention is so applied. .Here;.the grid..modulated Stage consists of two triodes VLt-vl'qwith tuned circuits Cl, LI and C2, L2 respectively between their cathodes and ."their anodesrthe'grids, which are connected to earth'through a condenser GC, being connected .:.together and to a source (not shown) of modulation input. The cathode tuned circuit Ll, Cl

forms; part of, a- .quarter wave, impedance invert- ,ing-- network .which also includes, in addition to a condenser C23, or. C23 ineach wire thereof, a tuned circuit L3,..,C3=connected betweenthean- 25 odesof ampair .of. triodes V2, V2 having grounded p. grids. ZIhis grounded ,gridstage is arranged in maccordancewiththis invention to present a high ..eiiectiveoutput impedance by providing the said v.stage, with a. high ,input impedance which isob- .3 ...t,ained, forhexample as shown, by couplingthe opposite endsof at uned .circuitL l, C4 connected .between. the ,.cathodes of the grounded. gridtri- ,odes V2,. V2 through blocking condensers BCI, A'QBCZand series resistancesSRl, SR2 to the op- .posite ends of a .tun'ed circuit L5, C5 connected 'between'the anodes of a; preceding pair oftriodes V3, V3 with grounded grids. High fret quency" input-is 1 applied at IN between suitably fchosen points' on the inductance of a parallel tuned circuit'Lfi; C6-between the cathodes :of the 1- triodes V3;-,V3."*Since-the load-here is-stabilised "by the resistances 'SRI SR2 the type of input --circuit for the triodes V3; V3 is unimportant.

A similar arrangement-to that of the last -de- 5 scribed embodiment can also 'beemployed if the modulated stage is an ordinary neutralised or 'screenrgridstage imposing avariable load by --reason of-change of grid current. indeed, anar- "rangement'in accordancewiththis invention-may she employedas a high-impedance source wherever -=required.

What is claimed-is: 1 1-.- A grounded grid amplifier --comprising a driven groundedgridrstage including two triodes imbalanced arrangementwith a tuned circuit be- :tween theiracathodes -andcanotherhtuned I circuit 1 in :parallelwith the load: between .theirzanodes, a :alow-impedancesource;forcdriving said stage includingtwo triodes: connected in a .balanced'cathcor-ode -;fol1ower;ci .cuit amt-havin a ;;tuned;- ci cui abetweenrthe two; cat o he of an an impedance inverting network; coupling said source -;;-to1n-saidrstage, said: {network including the two :tunedcirouitsgbetween thezcathodes of thesource c5 ra d he cathodes of e te ezrespectively.

I ...2.:-In-, an. amplifier;-system:.. an [electron dis- .Qharge \vdevice structure having a control, grid .rqWhiCh iS; .at, ground ,or. equivalent potential, said structurealso having-ananode in an output cir- 70..--.cuit .and a.-.cathode..whichis above ground .or

equivalent potential; a source of electricalen- I .ergytobeamplified, said source beingof low im- ;.,..pedance ,and comprising an. electron discharge ,,.tube structureqhaving; a control-grid excited by 75,,e1ectrical energy,- to., be.-.amplified,havi a. cath- REFERENCES CITED The following, references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,165,844 Finch July 11, 1939 Number Number Name Date Finch June 25, 1940 Conklin Aug. 13, 1940 Percival Nov. 24, 1942 Brown Sept. 21, 1943 Romander Jan. 29, 1946 Labin Nov. 25, 1947 Rosencrans Oct. 5, 1948 Wheeler Mar. 1, 1949 FOREIGN PATENTS Country Date France Feb. 18, 1941 

